Carburetor



Dec. 1934- J. R.-FISH 1,983,660

I CARBURETOR v Filed July 14, 1932' 7 Sheets-Sheet 1 INVENTOR. J'omv Roam? EsH BY j v Z ATTORN Ys.

' INVENTOR. i% Jwm RIIBERT ESH BY 7% I A TTORNEYS.

Dec. 11,1934. R, FI H 1,983,660

CARBURETOR Filed July 14, 1932 '7 Sheets-Sheet jZ/Z INVENTOR. Joy/v B0BERT 1 75/1 ATTORNEYS.

J. R. FISH CARBURETOR Dec. 11, 1934.

Filed July 14, 1932 7- Sheets-Sheet 7 Patented Dec. 11, 1934 UNITED STATES PATENT OFFICE signor .to National Equipment Company,

Springfield, Mass., a corporation of Massachusetts Application July 14, 1932, Serial No. 622,372

6 Claims.

This invention relates to carburetors for use upon internal combustion motors. One object of the invention is to improve the efliciency of existing carburetors. Another object is to simplify carburetor construction by making adjustment of the fuel-air mixture for different operating conditions dependent upon changes in differential fluid pressures inherent in the structure of the carburetor rather than depending upon changing mechanical adjustments, spring operated valves, multiple jet systems, or accelcrating pumps. Another object is to provide a carburetor which is self feeding even when the fuel supply is below the carburetor level. An-

]5 other object is to improve carburetor throttle construction. Another object is to improve the float valve operating mechanism. Another object is to provide a carburetor in which the fuel orifices are so large that foreign matter passing 20 through the screen cannot plug them. Other improvements in the structure and operation of the carburetor will be set forth in the following description and claims.

Referring to the drawings,

- Fig. 1 is an end elevation of a carburetor embodying the invention;

Fig.2 is a side elevation thereof; Fig. 3 is a central section through the carburetor, looking in the same direction as in Fig. 2;

Fig. 4 is a fragmentary detail of a screen; Fig. 5 is a detail of parts shown in Fig. 3, taken in difierent positions;

Fig. 6 is a sectional plan of the carburetor in let, with the float valve and its screen removed;

Fig. 7 is a section on line 7-7 of Fig. 6;

Fig. 8 is a detail of the. mechanism for operating the float valve; Fig. 9 is a top plan view of the of the carburetor;

Fig. 10 is a similar view with certain parts removed;

Fig; 11- is a central section shown in Fig. 3;

Fig. 12 is a section on line 12-12 of Fig. 11;

Figs. 13, 14, 15 and 16 are details similar to the upper portion of Fig. 3 but on a larger scale, illustrating various conditions under which the carburetor operates;

Fig. 17 is a detail of a modification;

Fig. 18 is a plan view of certain mechanism shown in Fig. 17;

Fig.19 is a detail of nozzle;

Fig. 20 is a detail showing a further modi- 55 fication; a

through a nozzle showing a modified form pp t.

Fig. 21 is a top plan view and a continuation of the devices of Fig. 20 and Fig. 22 is a partial View from the left in Fi 21.

The carburetor will first be described with reference to the form shown in Fig. 3. The body 21 of the carburetor is formed as an inverted bowl having a central tubular portion 22. Acupshaped base 23 is secured to the body 21 by a bolt 24 threaded into the tube 22. The base 23 serves as a sediment chamber and water trap, a perforated disk 25 serving to prevent disturbance of the sediment by the overlying liquid and a plug or valve 26 acting as a drain. One side of the base is formed as a chamber 27, closed at the end by a plug 28 and containing a cylindrical screen 29. A pair of small holes 30 are formed in the lower side of the chamber 27 so as to communicate with a passage 31"into which is threaded the fuel supply pipe 32. The top of this pipe is finished smooth, so as to receive a disk 33 acting as a check valve. This disk is loose within the passage 31, and is of such a diameter that it will cover the. hole in the pipe irrespective of its lateral displacement, thus preventing back flow; but is sufliciently smaller than the pipe to permit the forward passage of the liquid fuel around its edges. The holes 30 are made double so that it will be impossible for the disk 33 to rise under the influence of the as-' cending column of fuel and block off the opening into the chamber 27.

Within the chamber 27 is a valve member 35 having an axial passage through it formed to provide a valve seat for the conical end of a float controlled valve member 37. This member is grooved at 38 to permit the passage of fuel, and is pivotally connected at 39 to a yoked link 40 forming one member of a toggle (Figs. 3 and 8). The other link'41 of the toggle is pivotally connected at42 to a short rod 43,held adjustably in a bore 44 of the base 23 by a set screw 45. Links 40 and 41 straddle the central tube. 22, and "are pivoted at each side at 46 to a link 47 extending upwardly and secured to a cork or other float 48. If the float is of laminated cork, as is preferable, one way of joining the links to it is to turn the link ends over at right angles as at 49 and imbed them by pressure and cement in the body of the cork. Downward movement of the toggle to a point where it would be likely to-jam is prevented by its contact with the disk 25.

Subject to the fluid pressure conditions hereafter described the float controls the admission of fuel from the chamber 27 to the large chamber 50 within the body 21 of the carburetor. As the float descends the valve member 37 will be drawn away from its seat, increasing the fuel admission aperture. The action of the float valve may be controlled by loosening the set screw and adjusting the rod 43. As shown in Fig. 3, this adjustment is preferably arranged so that the set screw 45can only be reached when the base 23 is removed from the body portion 21, as it is only in this condition that the float parts are accessible.

The tube 22 has a central passage 51 connected with the float chamber by a removable plug 51' having a fuel metering hole 52 in it. At its upper end this passage 51 connects with a central passage 53 in a nozzle 54 shown best in Figs. 11 and 12, and connected by threads 55 with the top of the body 21. A gasket 54 is placed between the nozzle and the carburetor body, and a second one 55' at the conical bottom of the nozzle. A plurality of small air holes 56 are spaced at the side of the central passage 53, opening at their top within a shield 57, and at their bottom into an annular groove 58 formed in the nozzle and communicating with a lateral passage 59 in the carburetor body. In the example now under discussion, this passage is provided at its'outer end with a removable plug 60 having a small hole 61 through it. Plugs having various sized holes may be substituted until the one is found working best for the particular engine to which the carburetor is to be applied, or an adjustable needle valve may be used.

The upper end of the nozzle projects into the constricted section of a Venturi tube 65 having a flange 66 fitting air tight into a hood 68 and pressing against a shoulder 67 thereof. The hood is, as shown in Fig. 9, held to the body 21 by a plurality of screws 69. A groove 70 in the flange 66 is joined by a circumferential series of holes 71 with the interior of the Venturi tube'near its large end and is connected with the float chamber 50 by a passage 72 in the hood 68 and a tubular extension 73 of the carburetor body. The purpose of this connection is to preserve an equalized pressure between the interior of the delivery and of the Venturi tube and the interior of the float chamber with a result that will appear below. A gasket 73 (Fig. 13) is placed between the flange 66 and the shoulder 67, and the usual gasket 74, although in this case preferably of metal, is placed between the upper surface of the carburetor and the intake manifold 74'. When the carburetor is bolted to' the inlet manifold the pressure forces the flange 66, which initially extended slightly above the top of the hood 68, into the gaskets 73 and 74, thoroughly sealing it against leakage. The cylindrical body of the Venturi tube 65 extends upwardly into the intake manifold and is of somewhat smaller diameter leaving a circumferential pocket 76' the function of which will appear-below. This extension of the venturi prevents misalignment of its central aperture with that of the manifold and permits the use of a longer venturi without increasing the size of the carburetor. The hood 68 is formed with a flange 77' overlapping an upwardly extending flange 78'. These flanges serve to give to the incoming air stream a path preventing largely the sound waves generated within the carburetor from reaching the outer air.

Surrounding the cylindrical exterior of the Venturi tube 65 is' a throttle sleeve 75, also cylindrical in form and having its lower end beveled externally as at 76. A yoke lever 7'? is pivoted at 78 greatly varying pressure differentials.

to the carburetor body, its yoked portion 79 surrounding the throttle sleeve and having a pin and slot connection 80 therewith. An adjustable stop screw 81 limits the motion of the yoke lever in one direction, providing idling speed adjustment, while a boss 62 on the lever contacts with the carburetor body to limit motion in the opposite direction. The yoke lever maybe operated from any desired throttle lever or acceleration connection. When the sleeve is down (Fig. 13) it lies closely adjacent a shoulder 83 formed on the carburetor body.

The purposeof this bevel 76 is to modify throttie response. Manifold pressure being very low when the throttle is nearly closed, the amount of air passed by a given degree of throttle movement is relatively large. The beveled part of the throttle is within the recessed part of body during the first part of the throttle travel from closed to open position. The amount of air passing the throttle is determined by the clearance between the beveled part of the throttle and the shoulder or lip of the recess. Any degree of response is obtainable by the contour and clearance provided by this bevel. Fuel pressure on the needle 37 is greatestwhen motor is idling. Since the float mechanism merely maintains the fuel level and since the least fuel is required-at this time, toggle is nearly straight, providing maximum leverage. 0n full throttle, the fuel pressure is very low, fuel consumption maximum, the needle is farther from seat and toggle down to pass. increased amount of fuel, and leverage is minimum. Maximum leverage is provided when maximum pressure is to be overcome. This allows the use of a smaller float and maintains a more nearly constant fuel level in the face of As the float chamber fuel level must be high enough to overcome fuel pressure on needle when motor is running, and as this pressure becomes negative when motor stops, the needle is held firmly to seat by float mechanism, preventing back flow of fuel to main supply tank.

Formed at one side of the body 21 is a boss 85, having a shouldered hole 86 formed in it. Into the enlarged end of this hole a needle valve 87 is adjustably fitted. As shown the valve is thread ed into the hole. adjustment being obtained by rotating it, but the valve may if desired be fitted with a Bowden wire control from a remote point.

A hole 88 enters the hole 86 from the outside of the boss, providing an adjustable connection between the atmosphere and the chamber 50.

Since the'operation of the carburetor depends upon the variation of relative pressures at various places; a series of symbols of these different pressm'es will begiven before beginning a detail discussion of the several operating conditions.

1? is the pressure within the constricted throat of the Venturi tube 65. In this and other cases the pressure should not be considered as a constant, but as an instantaneous value to be compared with instantaneous values at other points at the same time. Q is the pressure within the top of the float chamber 50.

R is the pressure within the air passages 56. S is the pressure in the fuel line 32.

T is the pressure within the large end of the Venturi tube.

V is the pressure within the fuel nozzle 53. W is the pressure within the shield 57. A represents atmospheric pressure. When the engine is at rest P=Q=R=A, and

S=A+ the static head of the fuel in the line between the carburetor and the level of fuel in the supply tank. If they tank is higher than the carburetor S is always greater than A'and the level of thefuel in the chamber 50 is determined by the float in the manner common to gravity fed carburetors in general.- If the tank is lower than the carburetor, Sis always less than A; andwith the motor at rest would cause backflow to the tank except for the check valve 33 and the valve 37.

In the starting condition the valve 8''! is held open as in Fig.-l3,- giving a direct connection between chamber 50 and the atmosphere and making Q approach A fairly closely. At this time the throttle sleeve 75 is down, restricting the flow of air between the sleeve and the shoulder 83 and making P Q as a suction eifect is exerted by the rotation of the engine. This differential pressure causes the liquid fuel in the floatchamber to rise through the passages 51 and 53. At the same time air in the passage 59 is caused to flow through the holes 56 since R is greater than P,

mingling with the fuel coming out of the nozzle aperture 53 and'assi'sting in carrying it into the low pressure zone at the neck' of the Venturi tube. Due to the constriction in .the several air passages and the relatively large difierential between Q and W the fuel mixture is relatively rich, which is of course the condition desired. Under the extremely slow speed conditions present in starting the suction of the motor pulsates rather widely. As the suction drops the gasoline will tend to accumulate in the chamber 57 surrounding the central nozzle 53 (Fig. 11) When a suction pulse again is felt the air rushing through passages 56 will drive this gasoline forcibly through the venturi, effectively atomizing it and richening the mixture.

When the motor has started and is running. idle the same conditions prevail except that the valve 87 can be closed partialy or entirely. It is preferably left slightly open until the motor has warmed up and may then be closed. The adjustment of this valve serves as a means for controlling the carburetor accurately, both under starting and running conditions. In idling condition P T Q A. Also P R A. Flow of air and fuel takes place somewhat as before, except that the pressure Q has been reduced. If the static head in the fuel line is not too great, a matter readily controlled by design, Q S A; and, when thefloat drops sufficiently to permit, fuel will flow in past valve 37.

When the motor is idling the pressure Q is much more nearly equal to W than it was when the valve 87 was open, due to the fact that the chamber 50 is now substantially cut off from,

communication with the atmosphere and Q is dependent upon T rather than A. The motor, running with the throttle almost closed, acts as a suction pump, and maintains a somewhatpulsat-- partly by the air escaping within the hood 5'7,

from the holes 56. R exerts a much greater influence on V during idling than it does at other times, and raises W toa point where the differential pressure Q-W is only enough to make the fuel barely flow out. The fuelspilling out over the end of hole 53 is picked up by the air from holes 56 and carried up into the venturi.

The correct proportion of the various nozzle parts is of course dependent upon the particular typeof motor to which the carburetor is applied, and only general directions can be given. On account of the fact that the nozzle or jet 53 must be large enough to supply the maximum fuel requirements of the motor, it is much larger than the conventional jet used at idling speeds. If the jet opened directly into the throat of the venturi a slight increase of Q over P would cause the carburetor to flood when idling. The shield 57 is therefore provided, within which both the gasoline jet 53 and the air jets 56 open. Were the opening of .the shield into the venturito be very small in size, the pressure W in the shield would become superior to Q, due to the connection to the atmosphere through ducts 56. This would of course cause a' flow of air down through the duct 53 into the float chamber. By increasing the size of the opening of the shield into the venturi the pressure W may be brought to the desired balance, where it is less than Q but greater than P. .W thus acts as a brake on the difierential QP to control the mixture, the amount 'of braking action being regulable by changing of the carburetor. Reducing the diameter of the venturi throat produces a similar eifect. There is a limit to the distance it is desirable to' go in this direction, however, as the differential between Q and P is the main fuel metering pressure feed- 11% fuel into the air stream and this differential is reduced by moving the holes 71 toward the venturi throat. A suitable compromise can be found readily by trial for the particular type of motor to which the carburetor is to be applied. The location shown in the drawings has been found suitable in practice for a small fou'r-cylinder motor.

One other effect results from the depression of Q during idling. As stated above, the pressure S is equal to A less the static head .of fuel if a depressed tank is used. This static head is usually only a few inches of gasoline, not a large amount. Any material depression of Q below A will cause flow of fuel past the valve 37 provided the position of the float permits. One advantageous feature of the float construction may be referred to in this connection. When the valve 3''! is closed the toggle 40, 41 is substanw tially straight, offering the greatest resistance to displacement by pressure of fluid behind it. If

the float drops the toggle is bent, making the valve subject to still further displacement if there is a difierential between S and Q. Conversely, even though there may be a considerable differential fluid pressure the float will have no did-- culty in cutting off the fuel supply when the float chamber is-full. This contrasts favorably with the usual single lever valve control, in which fluid pressure is as effective as float position in permitting flow of fuel through the valve. During operation of the motor the differential pressure SQ forces the valve 3'7 off its seat, working through the toggle to depress the float in the gasoline a greater amount than would occur under static conditions. When the motor stops this differential pressure is reversed in direction (with a depressedfuel supply) giving the float a chance to rise with a result that the valve 37 is pressed against its seat with sufficient force to prevent back flow even without the check valve 33.

When the throttle is opened to cause acceleration of the motor there is a period of speed pickup during which the throttle opening may be considered abnormally large with respect to the motor speed. During this period different mixture conditions are required than for wide throttle openings at high speed, a rich mixture giving slower combustion and greater power. During idling operat ons gasoline will accumulate in the pocket '76 surrounding the Venturi tube, and in a pocket 60' between the shield 5'7 and the throttle '75. The first rush of air occurring when the throttle is suddenly opened sweeps the fuel out of these pockets and assists in securing proper mixture conditions at the start of the engine's acceleration.

Assuming now that the throttle is widely open and the engine turning over very slowly, P, T, and Q are all very nearly equal to A on account of the free access of atmospheric air into the bottom of the venturi. P will, however, be lower than T on account of the venturi effect, and also lower than Q on account of the connection '73 be-' tween T and Q. Under these conditions the differential between W and V is much lowered, and the braking effect of W vanishes. In fact, the air rushing through the ducts 56 mixes with and emulsifies the fuel coming out through duct 53, making it lighter and easier to be carried through the venturi by the air coming from the throttle. Pressure conditions are such that during this period of wide throttle and slow speed a rich mixture is supplied to the motor.

As the speed of the motor increases the pressures P, T, and Q all decrease due to the greater flow of air and the consequent higher resistance offered by the passages. The differential between P and T also increases, P diminishing in response to the increased venturi effect increasing the fuel supply. The increased differential between P and T increases the fuel supply about in equal ratio to the increased air supply. As the pressure drops, W becomes progressively more effective as a retarding force, leaning out the mixture in proportion to the increased air flow responsible for the pressure drop. The venturi should be large enough to supply maximum air requirements of the motor. This condition is reached at maximum R. P. M. at full throttle. A smaller venturi makes for better acceleration, self-feeding, and, within limits, for high speed. The main fuel metering jet 51 should be large enough to supply suflicient fuel at maximum R. P. M. at full throttle. The opening into the venturi from the shield should be large enough to pass sufficient fuel at full throttle, but running at minimum R. P. M.; then P, T, Q, R, V, W are substantially equal but not actually to each other and to A. Therefore the fuel feed is in proportion to the relative size of 56, 51, and 53, Q, V.

being very nearly equal to A; the retarding force aesaeeo at W has disappeared; and air coming from 56 mixes with the fuel and assists its discharge.

56 and 61 must be large enoughto produce a pres-- sure at W which will supply the correct idling mixture when all other operating requirements are met. A hole 61, small enough to underfeed 56 causes a rich mixture at intermediate speeds. One large enough to overfeed 56 causes a lean mixture at intermediate speeds. A high float chamber fuel level enriches idling and the low speed full throttle mixture is also enriched. Holes 56 should be so proportioned to 53 and the nozzle opening above 53 as to allow fuel to drop into the annular chamber surrounding 53 during running of the engine with the throttle partially open, allowing the violent air jet escaping from 56 to atomize the fuelthroughly. It will be observed that under all the motor conditions the proper mixture conditions are obtained automatically and not by mechanically operated cams, nozzles, or the like. The response of the carburotor is more rapid than was possible with carburetors of the mechanically operated type, not only improving the motor pick-up, but causi g the carburetor to respond automatically to cyclic pressure variations in motor operation. The e!- flciency of the carburetor, and consequently the gasoline mileage, is much increased.

Throughout the different phases of operation the pressure Q remains somewhat sub-atmospheric, so that a. differential pressure is created which causes fuel to fiow into the float chamber from the line. The difierential decreases when the pressure Q approaches atmospheric, as it does in starting and full throttle conditions. Owing to the large supply of fuel normally in the float chamber, these conditions above described do not last long enough to cause any harmful depletion of the fuel. If the throttle is partially closed even momentarily what depletion has occurred will be fully compensated, it being only a matter of a few seconds to completely fill the carburetor.

In Fig. 1'7 a modification has been shown in which the admission of air through the passage 59 is thermostatically controlled. In this form an adjustable needle valve is substituted for the fixed nozzle 60 and instead of air being admitted directly from the atmosphere it reaches the needle valve 90 through a pipe 91'. This pipe opens into a chamber 92 in a casing 93 secured to the exhaust pipe 94 of the motor. A second needle valve 95 is held by a spring 95' so as to shut off the chamber 92 from inlet ports 96 except .when it is positively moved by an expansive thermostatic element 9'7. With this arrangement the supply of air 'to passage 59 is shut off when the motor is cold, increasing the differential pressure VW and allowing Q to force suflicient'fuel through the nozzle opening 53 to start the motor. As the motor warms up the valve 95 is opened by the thermostat, gradually leaning the mixture as the motor temperature permits. When the thermostat'control is used the valve 8'7 is either eliminated or is left closed or but slightly open. r

In Fig. 19 is shown a modification of the nozzle by which fuel is injected into the throat of the Venturi tube. In thiscase the nozzle is composed of a body portion 100 screwed into the carburetor body 21 'and provided with a central axial bore 101 similar to the bore 53. The passage 59 communicates with an annular recess 102, which in turn communicates with the bore 101 through one or more radial ho1es103. In the operation of this type of nozzle the air mixes the boss 112 by a set screw 117'and contains a.

' with the fuel during its passage up the bore,

slidable in a bore 111 providedin a. boss 112.

A conical end 113 on the slide fitsinto a hole 114 communicating with the interior of the float chamber, thereby controlling the flow of air through .a port 115. A cap 116 is secured to spring 118 normally urging the slide 110 towards closed position. A Bowden wire 119, passing iii! of the mixing point,

through a sheath 120, is secured in the slide 110 by a set screw 121, the sheath being held by a clamp screw 122.

At its other end the sheath 120 is secured by a screw 125 to a bracket 126 having a threaded portion 127 extending through the mounting 128 and held by a lock nut 129. The wire 119 is pinned to a slide 130 extending through the bracket and threaded at its other end into a handle 131, a set screw 132 holding it fixed in position. A collar 1331s threaded, on. the extension 127 of thebracket and is held in adiusted position by a friction spring 134. If desired, the collar may be provided with an areshaped slot 135 into'which projects a pin 136 secured to the lock nut 129, so that the collar can be rotated only between predetermined In use the collar 133 is adjusted to give the amount of opening of valve 110 desired for running of the motor. 'When it is desired to produce a choking effect as described above, the tile 131 is pulled out in the same way as the usual choke control, pulling on the Bowden wire against the force of spring 118 to unseat the slide 110 and admit air to the float chamber.

In Fig. 20 I have also shown an air cleaner placed under the flange 77'; comprising aperforated tube 140 filled with copper shavings 141 or other air cleaning material.

While I have described the invention in considerable detail and have indicated but a few specific ways in which it may be modified tomeet particular circumstances, it will be understood that many changes can be made by those skilled in the art without departing from the invention as defined in the claims set forth below. Furthermore, while I have in some instances set forthmy best understanding of the theory underlying the operation of the carburetor, that understanding may in some instances be imperfect. The practical advantages of the carburetor have been proven by actualtest, and I do not intend to be restricted by any lack of complete understanding of the theoretical grounds for these advantages.

It will be observed that the usual throttlev is completely eliminated, its;.place being taken by the annular throttle 75, 83 which is located ahead The air is thus caused to travel upwardly through the Venturi in a uniform column, increasing the efliciency both by reducing air friction and by facilitating uniformity in the mixture of air and fuel. vDue to the location of throttle on atmospheric side of the venturi, the pressure and density of air in the venturi is very low duringpart throttle operation. As the density is low, velocity-is high. Atornized fuel discharged from nozzle into this air stream practically explodes into a vapor. Condensation of fuel on the throttle and deflection of fuel from'it onto the manifold walls are also avoided. f

What I claim is: A 1. A carburetor. comprising a fuel chamber, a

Venturi tube spaced from the fuel chamber so as to have substantially circumferential connec tion'with thev atmosphere at its end adjacent the .fuel chambena throttle sleeve slidableyover the as to have substantially circumferential connection with the atmosphere at its end adjacent the 'fuel chamber, a throttle sleeve slidable over the Venturi tube to regulate the extent of opening of said connection, the second end of the Venturi tube being connected to the intake manifold of an engine, a nozzle opening into the throat of the Venturi tube and connected to the fuel chamber beneath the fuel level thereof, a connection between the atmosphere and said' nozzle, and a connection between the second end of the Venturi tube and the fuel chamber.

3. A carburetor comprising a: fuel chamber, a Venturi tube spaced from the fuel chamber so as to have substantially circumferential connection with the atmosphere at its end adjacent the fuel chamber, a throttle sleeve slidable over the Venturi tube to regulate the extent of opening of said connection, the second endof the Venturi tube being connected to the intake manifold of an engine, a fuel duct opening into a shield, the latter opening into the throat of the Venturi tube, said fuel duct connected to the fuel chamber beneath the fuel. levelthereof, a shield surrounding the opening of the fuel duct, 8. connection betube spaced fromthe float chamber so as to have substantially circumferential connection with the atmosphere at its end adjacent the float chamber,

a throttle sleeve slidable over the Venturi tube to regulate the extent of opening ofsaid con-' nection, the second end of the Venturi tube being connected to the intake manifold of an engine, a nozzle opening into the throat of the Venturi :tube and connected -to the fuel chamberbeneath the fuel level thereof, and a connection between the second end ofthe Venturi tube and the fuel chamber whereby the pressure in the fuel chamber will during therunning of the engine, be

maintainedbelow the pressure in the fuel supply but above the pressure at the opening of the nozzle.

5. A carburetor comprising a Venturi tube-con.- nected to the intake manifold of an engine, an annular air inlet at the opening of said tube, an annular throttle regulating said inlet, a fixed nozzle opening into the low pressure zone of the Venturi tube and connected to the fuel chamber, and an air connection between thesides of the Venturi tube remote from the throttle and the fuel chamber whereby the difierential pressure on the fuel I at the epening of the nozzle will be responsive to the rate of flow of air through the ftenturi tube.

6. A carburetor comprising a. Venturi tube connected to the intake manifold, an annular throttle slidable over the Venturi tube and having its outer edge beveled, a shouldered member against which the throttle is adapted to move to close ofi thev admission of air to the Venturi tube, the air passing between the beveled portion of the throttle and the shouldered part of said member when the throttle is in nearly closed position, and

a fuel nozzle opening into the low pressure zone of the Venturi tube.

1 JOHN ROBERT FISH. 

